This invention relates, in general, to methods automatically inspecting items, and more particularly, to a method for automatically inspecting a semiconductor package.
During the assembly of components in a manufacturing cycle it becomes necessary to verify the location, alignment, and condition of articles being used in the cycle. This is particularly true in an automated or semiautomated assembly cycle. In the manufacture of semiconductor devices it is particularly important to inspect the semiconductor package before shipping to ensure that the package is free of voids, foreign material, and that leads which extend from the package are in proper alignment. Recently, solid state television cameras have been used to visually monitor semiconductor packages. The data from the camera can then be processed in a digital manner to determine the coordinate location of the semiconductor package and leads. However, the manner in which the data is processed determines speed, accuracy, and robustness of the monitoring system.
Digital processing of a visual image involves reducing a large amount of image data to a minimum data set while retaining information about important characteristics of the package. Important characteristics are package dimensions and spacings which must meet predetermined specifications, as well as data which represents anomalous shapes caused by debris and manufacturing defects. Specified data includes such things as lead spacing, lead alignment, and package size. Anomalous data includes the location and size of voids, cracks, chips in the package or foreign matter such as excess ink on the package. To determine the acceptability of the semiconductor package under inspection the data set must be compared to some standard or specification. In the past, this standard has been determined by recording and processing a visual image of a number of packages which were known to be acceptable. These images could then be used as a standard to which the image of a package under inspection could be compared. One problem with this technique, however, is that images are very sensitive to background lighting, reflectivity, and magnification of the image under inspection. Since these conditions are quite variable in a production environment, image comparison or image correlation techniques are difficult to use in a production inspection operation and require a great deal of manual intervention.
Accordingly, it is an object of the present invention to provide an improved method of manipulating data to automatically inspect a semiconductor package.
Another object of the present invention is to provide a method to automatically inspect a semiconductor package and leads in a manner that is fast and accurate.
Yet another object of the present invention is provide a method to analyze visual data against a predetermined specification in a real time fashion.
A further object of the present invention is to use direction edge correlation techniques to identify key features of a semiconductor package.
Still another object of the present invention is to use morphological dilation techniques to increase the robustness of an image analysis system.